Abstract: M33 contains a large number of emission nebulae identified as supernova
remnants (SNRs) based on the high [S II]:Ha ratios characteristic of shocked
gas. Using Chandra data from the ChASeM33 survey with a 0.35-2 keV sensitivity
of about 2 x 10**34 ergs/s, we have detected 82 of 137 SNR candidates, yielding
confirmation of (or at least strongly support for) their SNR identifications.
This provides the largest sample of remnants detected at optical and X-ray
wavelengths in any galaxy, including the Milky Way. A spectral analysis of the
seven X-ray brightest SNRs reveals that two, G98-31 and G98-35, have spectra
that appear to indicate enrichment by ejecta from core-collapse supernova
explosions. In general, the X-ray detected SNRs have soft X-ray spectra
compared to the vast majority of sources detected along the line of sight to
M33. It is unlikely that there are any other undiscovered thermally dominated
X-ray SNRs with luminosities in excess of about 4 x 10**35 ergs/s in the
portions of M33 covered by the ChASeM33 survey. We have used a combination of
new and archival optical and radio observations to attempt to better understand
why some objects are detected as X-ray sources and others are not. We have also
developed a morphological classification scheme for the optically-identified
SNRs, and discuss the efficacy of this scheme as a predictor of X-ray
detectability. Finally, we have compared the SNRs found in M33 to those that
have been observed in the Galaxy and the Magellanic Clouds. There are no close
analogs of Cas A, Kepler's SNR, Tycho's SNR or the Crab Nebula in the regions
of M33 surveyed, but we have found an X-ray source with a power law spectrum
coincident with a small-diameter radio source that may be the first pulsar-wind
nebula recognized in M33.

Comments:

142 pages, including 8 talbes and 50 figures, to be published in ApJ Supplements